In a case where a thermoplastic resin composition is used for various applications such as housings of a personal computer and a display device, an electronic device material, and automotive exterior and interior parts, there sometimes occurs a problem that it is difficult to release generated heat because a plastic is less thermally conductive than an inorganic substance such as a metal material. In order to solve the problem, an attempt has been extensively made to obtain a highly thermally conductive resin composition by blending, with a thermoplastic resin, a highly thermally conductive filler in a large amount. In order to obtain a highly thermally conductive resin composition, it is necessary to blend, with a resin, a highly thermally conductive filler such as graphite, carbon fiber, alumina, or boron nitride generally in an amount of not less than 30 vol %, and further in a high amount, i.e., in an amount of not less than 50 vol %. However, thermal conductivity of a resin composition is limited even if a large amount of thermally conductive filler is blended to a resin because the resin itself has low thermal conductivity. In view of the circumstances, improvement in thermal conductivity of a resin itself is demanded.
Patent Literature 1 discloses an epoxy resin as a thermosetting resin itself having excellent thermal conductivity. The resin is thermally conductive to some extent, whereas it is difficult to produce the resin because the resin has a complicated molecular structure. Patent Literature 2 discloses an epoxy resin which is synthesized with relative ease, however, does not have enough thermal conductivity.
A thermoplastic resin is exemplified by a resin molded product described in Patent Literature 3. The resin molded product is obtained as follows: thermal liquid crystal polyester is oriented by at least one external field selected from a flow field, a shear field, a magnetic field, and an electric field, so as to cause the thermal liquid crystal polyester to be highly thermally conductive in a direction in which the thermal liquid crystal polyester is oriented. The resin molded product is highly thermally conductive in one axis direction but less thermally conductive in the other two axis directions. In addition, in the case of the magnetic field, at least 3 teslas of magnetic flux density is required to obtain a desired thermal conductivity. This makes it difficult to produce the resin molded product.
There have been no other examples of research report on a thermoplastic resin which is not subjected to a special molding process such as extension or magnetic field orientation and in which resin itself is highly thermally conductive. As for a liquid crystalline thermoplastic resin, Non Patent Literatures 1 to 4 describe alternating polycondensation products, showing liquid crystal phases, which are formed from mesogenic groups and alkyl chains. However, none of the Non Patent Literatures describe thermal conductivity of such liquid crystal thermoplastic resins, and ends of the liquid crystal thermoplastic resins are not sealed. It is therefore difficult to produce a material (A) whose molecular weight is changed as polymerization of the material is progressed when the material is melted (e.g., when the material is subjected to extrusion mixing or injection molding) and (B) which has stable properties.
Patent Literatures 4 and 5 disclose each liquid crystal polyester whose molecular chain end is sealed. However, each liquid crystal polyester has low crystallinity because of its molecular structure, so that a resulting resin itself has low thermal conductivity.